3run: I think you just have somehow the wrong approach. You're permanently complaining about problems in your game and expect that other people fix that for you. Instead you should just learn to use your tools.

All raycast cars determine the ground distances by casting rays from the wheel centers to the ground. The wheel will move upwards immediately when its center goes over a 90 degrees border, because then the distance changes suddenly. This is just logical and has nothing to do with a "bug". You can see this in hundreds of games. In a few games you won't see this because they don't use raycast cars or the level designer has hidden that effect with a solution as suggested by Superku.

Either be content with the current solution, or go and learn and improve it. With merely complaining you won't achieve anything.